實現(xiàn)思路：

1，首先要拿到window (方式有多重可以app delegate,或者創(chuàng)建window失受、keywindow等等方式)讶泰。
2. 然后創(chuàng)建一個backgroundView，使其frame和window相等拂到，設(shè)置背景顏色痪署，再添加到window上。
3.把需要顯示的view添加到backgroundView上兄旬，當然有動畫效果更好狼犯，通過改變view的frame來實現(xiàn)view的顯示與隱藏。

代碼如下

#define SCREENWIDTH  [UIScreen mainScreen].bounds.size.width
#define SCREENHEIGHT  [UIScreen mainScreen].bounds.size.height

#import "ViewController.h"
@interface ViewController ()
@property (strong, nonatomic)UIView *bgView;//半透明背景
@property (strong, nonatomic)UIView *alertView;//假設(shè)為彈窗
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    UIButton *btn = [[UIButton alloc]initWithFrame:CGRectMake((SCREENWIDTH-100)/2, 50, 100, 100)];
    btn.backgroundColor = [UIColor yellowColor];
    [self.view addSubview:btn];
    [btn addTarget:self action:@selector(show) forControlEvents:UIControlEventTouchUpInside];
}
- (void)show{
    //1. 取出window
    UIWindow * window = [[UIApplication sharedApplication] keyWindow];
    //2. 創(chuàng)建背景視圖
    _bgView = [[UIView alloc]init];
    _bgView.frame = window.bounds;
    //3. 背景顏色可以用多種方法
    _bgView.backgroundColor = [[UIColor blackColor]colorWithAlphaComponent:0.4];
    //    _bgView.backgroundColor = [UIColor colorWithWhite:0.1 alpha:0.6];
    [window addSubview:_bgView];
    //4. 把需要展示的控件添加上去
    _alertView = [[UIView alloc ]initWithFrame:CGRectMake(0, SCREENHEIGHT, SCREENWIDTH, 49)];
    _alertView.backgroundColor = [UIColor greenColor];
    [window addSubview:_alertView];
    //5. 動畫簡單(low)
    [UIView animateWithDuration:0.3 animations:^{
        _alertView.frame = CGRectMake(0, SCREENHEIGHT-49, SCREENWIDTH, SCREENHEIGHT);
    }];
    //6.給背景添加一個手勢，后續(xù)方便移除視圖
    UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(hideAlertView)];
    [_bgView addGestureRecognizer:tap];
}
- (void)hideAlertView{
    //動畫簡單(low)
    [UIView animateWithDuration:0.3 animations:^{
        _alertView.frame = CGRectMake(0, SCREENHEIGHT, SCREENWIDTH, 49);
    }];
    // 延遲幾秒移除視圖
    [self performSelector:@selector(remove) withObject:nil afterDelay:0.3];
}
- (void)remove{
    [_bgView removeFromSuperview];
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


@end